ABSTRACT: Catharanthus roseus, family Apocynaceae is a large deciduous plant. The present work highlights the use of vinca flower extract as acid base indicator in different types of acid base titration. The equivalence points obtained by the fruit extract coincident with the equivalence point obtain by standard indicator. In case of weak acid and weak base titration, the results obtained by the flower extract matched with the results obtained by mixed indicator. This natural indicator is found to be a very useful, economical, simple and accurate for said titration.

INTRODUCTION: Catharanthus roseus is known as Madagascar periwinkle. This plant was formerly classified as the species Vinca rosea, Lochnera rosea and Ammocallis rosea1. This periwinkle is a perennial evergreen herb in the dogbane family (Apocynaceae) that was originally native to the island of Madagascar. It has been widely cultivated for hundreds of years and can now be found growing wild in most warm regions of the world, including the Southern U.S2-3. The plants grow one or two feet high have glossy, dark green leaves (1-2 inches long) and flowers all summer long. Horticulturists have developed varieties with colors ranging from white to hot pink to purple. The plant has historically been used to treat a wide assortment of diseases. It was used as a folk remedy for diabetes in Europe for centuries. In India, juice from the leaves was used to treat wasp stings. In Hawaii, the plant was boiled to make a poultice to stop bleeding. In China, it was used as an astringent, diuretic and coughs remedy. In Central and South America, it was used as a homemade cold remedy to ease lung congestion and inflammation and sore throats. Throughout the Caribbean, an extract from the flowers was used to make a solution to treat eye irritation and infections. The plant contains a mother lode of useful alkaloids (70 in all at last count). Some, such as catharanthine, leurosine sulphate, lochnerine, tetrahydroalstonine, vindoline and vindolinine lower blood sugar levels (thus easing the symptoms of diabetes). Others lower blood pressure, others act as hemostatics (arrest bleeding) and two others, vincristine and vinblastine, have anticancer properties. Periwinkles also contain the alkaloids reserpine and serpentine, which are powerful tranquilizers. In the 17thcentury chemist Robert Boyle, described indicators extracted from roses and other plant materials in his book “The Experimental History of Colors” published in 16644. Boyle included the ability to turn plant juices red among the properties of acids. The possibilities listed were only a few of many. Almost any highly colored fruit or vegetable or flower petal has the potential for use as an acid base indicator. Acid-base indicators are commonly employed to mark the end of an acid-base titration or to measure the existing pH of a solution. These are substances that reveal, through characteristic color changes, the degree of acidity or basicity of solutions. Indicators are weak organic acids or bases that exist in more than one structural form (tautomers) of which at least one form is colored. Intense color is desirable so that very little indicator is needed; the indicator itself will thus not affect the acidity of the solution. Care must be used to compare colors only within the indicator range. The indicator range is the pH interval of color change of the indicator. Some are most common indicators used for beginning chemistry, because its color change is very obvious which makes it easy to use. A pH indicator is a halochromic chemical compound that is added in small amounts to a solution so that the pH (acidity or alkalinity) of the solution can be determined easily. Hence a pH indicator is a chemical detector for hydronium ions (H3O+) (or Hydrogen ions (H+) in the Arrhenius model). Normally, the indicator causes the color of the solution to change depending on the pH5.In this study we observed the reaction of flower extract in different pH conditions and compared natural indicator to commercial indicators with measurement of pH. MATERIALS AND METHODS: Analytical grade reagents were procured from Tatyasaheb Kore College of Pharmacy, Warananagar Tal-Panhala Dist-Kolhapur.Reagents and volumetric solutions were prepared as per I.P. The flowers of vinca were collected and authenticated. The petals were separated from whole flower and used for further study. Four gm of petals were macerated for 15 min with 20 ml methanol6. After pressing the mark, filtrate was collected. By repeating same procedure with same solvent the extract was concentrated. Finally extract was filtered and used as indicator. The experiment was carried by using the same set of glassware for all type of titrations. As the same aliquots were used for both titrations i.e. titration by using standard indicators and flower extract, the reagent were not calibrated. The equimolar titrations were performed using 10 ml of titrant with three drop of indicator. All the parameters for experiment are given in Table1. A set of five experiments was carried out and mean and standard deviation was calculated from results. The flower extract was screened for its use as an acid base indicator in acid base titration7, and the results of this screening were compared with the result obtained by standard indicators (methyl red, phenolphthalein and mixed indicator) for strong acid strong base (HCl and NaOH), Strong acid weak base (HCl and NH4OH), weak acid strong base (CH3COOH), weak acid weak base (CH3COOH and NH4OH) titrations. The results of screening were listed in Table1. RESULTS AND DISCUSSIONS: For all titrations the equivalence point obtained by the fruit extract coincident with the equivalence point obtain by standard indicator while in case of weak acid and weak base titration, the results obtained by the flower extract matched with the results obtained by standard indicator. But it is noted that the flower extract is beneficial for weak acid and weak base titration because it involves use of mixed indicator, while the fruit extract can be used alone in such titrations. ACKNOWLEDGEMENT: The authors would like to thank Principal Tatyasaheb Kore College of Pharmacy, Warananagar Tal- Panhala Dist- Kolhapur for providing laboratory facilities.